The present invention relates to a small turbo compressor. More particularly, it relates to a small turbo compressor which is capable of providing clean compressed air excluding oil and enhanced energy efficiency.
Air compressors for industrial use are characterized as reciprocating, screw and turbo compressors. The reciprocating, screw and turbo compressors are used for less than 50 horsepower (hp), about 50 to 200 hp., and over 600 hp., respectively. The turbo compressor is of excellent durability and provides clean air excluding oil as compared with reciprocating and screw ones, and is superior to them. However, since there is a limit to the development of gear techniques, a turbo compressor of less than 600 hp. has not been manufactured, and Japanese IHI that developed the 110,000-RPM increasing gear mechanism first proposed a 100-hp turbo compressor. The turbo compressor which depends on the quality of the increasing gear cannot be manufactured to a small size of less than 100 hp. In the presently-available turbo compressor since impellers are driven by a motor and an increasing gear, the outlet width of an impeller of the final stage compressor becomes too small, and there is a limit to being in a high compression ratio with a small amount of gas. For example, when trying to produce gas of 10 bar by a 200-hp turbo compressor, the outlet width of the impeller of the final stage compressor is about 2 mm, so an axial clearance cannot be secured and the efficiency of the final stage compressor is too low to be of practical use. Even in case of producing a pressure of 20 bar by a 500-hp turbo compressor, it cannot operate because of the same reason as the above.
Therefore, in spite of various advantages of the turbo compressor, it cannot be used for less than 200 hp.
In order to realize a turbo compressor with a small amount of air, the present invention employs compressors driven by an external power and a turbine driven by a part of the compressed air, and connected to the final stage of the compressor to produce about a pressure of 11 bar with a small amount of gas. For low-stage compressor such as a first-stage or second-stage compressor, their impellers are driven by a conventional method such as increasing gear, and a high-stage compressor (third-, fourth-, and final stage compressor) employs a turbine driving mechanism using compressed air produced from the low-stage compressor in order to provide the satisfactory rotational speed not to decrease the outlet width of the impeller of the high-stage compressor in case of a small amount of gas (generally, less than 1.0Kg/sec). According to a conventional gear driving, the rotational speed can hardly exceed 70,000 RPM because of the limit of gear mechanism, and in order to produce a high compression ratio with the small rotational speed, the outlet width of the impeller becomes small, which cannot be of practical use.
It is an object of the present invention to provide a small turbo compressor which can obviate disadvantages of conventional compressor techniques, and assures an increase in energy efficiency, supply of clean compressed air, and satisfactory operation in a high compression region with a small amount of gas.
In order to achieve the above object, the present invention provides a multi-stage turbo compressor including
a turbine driven by a high-pressure gas from a low-stage compressor""s outlet; and a high-stage compressor driven by a power transmitted through an axis directly connected to the turbine. The gas that passed the turbine is returned to a first-stage compressor""s inlet. First and second compressors are driven by a high-speed motor directly connected thereto. Or, the first and second compressors are driven by a motor whose rotational speed is increased by an increasing gear.